[Three-dimensional finite element analysis of the effect of the location and diameter of implants on the stress distribution in three-unit implant-supported posterior cantilever fixed partial dentures under dynamic loads].

OBJECTIVE: To examine the effect of the location and diameter of implants on stress distribution in three-unit implant-supported posterior cantilever fixed partial dentures (FPD) in the mandible.

METHODS: A three-dimensional finite element model was developed to represent a rigid implant-supported posterior FPD that restores the second left premolar, first molar, and second molar. The location of the distal implant with a diameter of 4.8 mm remained the same, whereas the mesial implants with diameters of 4.1 and 4.8 mm were successively moved toward the posterior area with distances of 5.5, 8.0, 10.5, and 13.0 mm from the long axis of the mesial implants to the first premolar to form the cantilever FPD. Dynamic loads of 250 N were applied from different directions on the buccal and lingual cusps of the FPD to simulate the masticatory cycle for 0.875 s. The maximum Von Mises stresses were calculated using the finite element analysis software MSC. Marc and Partran.

RESULTS: The maximum Von Mises stresses of the mesial and distal implants increased to some extent as the mesial implants moved toward the posterior area. Significant increases in the maximum Von Mises stresses were obtained when the mesial implants were located more than 8.0 mm posterior to the first premolar, and moderate increases in the stresses were observed when the mesial implants were located less than 8.0 mm posterior to the first premolar. The use of a broader implant reduced the stress on the interface between the bone and the implants. The maximum Von Mises stresses were found in the cervical region of the cortical bone adjacent to the mesial or the distal implants during stages II to IV of the masticatory cycle. Off-axial loading induced more stresses compared with vertical loading.

CONCLUSION: The location of implants in three-unit implant-supported posterior cantilever FPD is a significant factor that influences the stress generated in the interface between the bone and the implants. An implant-supported cantilever FPD is a feasible option for restoring missing teeth when the length of the cantilever is not greater than the width of a premolar. Two important factors should be considered before choosing the implant diameter, namely, bone volume and cantilever length.